1. Field of the Invention.
The present invention relates to the field of thermal or dry film processing and, in particular, to a dry film developer and to an associated process for heating the film to the development temperature by stretching the film across a curved heated surface.
2. State of the Dry Film Aperture Card Printing Technology.
Heat processed, dry films are known wherein images recorded on the film are developed by heating the film to its developing temperature. One example of such a dry film is the Recordak Dacomatic.TM. DL Film 2471 available from/manufactured by the Eastman Kodak Company of Rochester, N.Y.
The application of interest here for such dry films is computer assisted design and, more specifically, the recording of computer-generated or stored drawing or design information on a frame of dry film mounted on an aperture card using an automated aperture card printer. Referring to FIGS. 1 and 2, a typical aperture card 10 comprises a rectangular body 11 of cardboard or paper stock or other suitable material having an identification strip 17 and a rectangular aperture 12 within which is mounted a frame 13 of dry film. As shown most clearly in the enlarged non-scale cross sectional representation of FIG. 2, the film 13 comprises a base or body 14 of polymeric material such as Mylar.TM. or of other suitable material which is transparent to the exposing radiation and a layer 16 of photosensitive emulsion. In the printer, the image is recorded by exposing the film to a scanned laser, then is developed by heating the film to its developing temperature. Such an automated aperture card printer is described in copending commonly assigned U.S. patent application No. 042,210 entitled "An Aperture Card Plotter" filed Apr. 24, 1987 in the name of the inventors Semyon Spektor, Robert J. Grady, Michael H. Ranger, Wilson S. Chinn, Alexander J. McKennon and Samuel D. I. Emerson, III. A dry film developer for this automated aperture card printer is described in co-pending commonly assigned U.S. patent application Ser. No. 036,517 entitled "A Dry Film Developer For An Aperture Card Printer" filed Apr. 9, 1987 in the name of inventors Semyon Spektor, Michael Veprinsky and Michael H. Ranger. These patents are incorporated by reference in their entirety.
FIGS. 3-5 depict the referenced Spektor et al., dry film developer. A heater block assembly 20 which is provided with an arcuate projecting heating surface 22 is rigidly affixed to the ends of rods 24 mounted to base 26. The curved central portion of the heater block assembly 20 houses an electrical resistance heater 27 (FIG. 5). A spring-loaded bearing block 29 which has a recessed area 31 is slidably mounted on the two rods 24, with the associated springs 28 mounted on the rods between the heater block assembly 20 and the bearing block 29. The bearing block contains a set of guide surfaces 32 for receiving the aperture card 10.
Referring in particular to the FIG. 5 view of the front of the dry film developer, four sleeve bushings 34 extend through the heater block assembly 20 on each side of the central portion. Spring-loaded fingers 37, having arcuate gripping surfaces 38, are slidably mounted within the sleeve bushings 34. The gripping surface 38 are positioned so as to contact the aperture card 10, on each side of the frame 13 of dry film, when the bearing block 29 is urged upwardly toward the heater block assembly 20. The gripping surfaces 38 are triangularly shaped with the tips of the triangles positioned parallel to the arc of the arcuate surface 22.
In operation, as the tips of the gripping surfaces 38 contact the aperture card 10 and are urged into further contact, the tips bend outward, stretching the film 13. The stretching provided by the gripping surfaces 38 is perpendicular to the stretching provided by the arcuate heating block surface 22. The combined stretching enhances contact between the film 13 and the heated surface 22.
Referring to FIGS. 3 and 4, various mechanisms may be used to urge the bearing block 29 into the developing position. The preferred embodiment of the referenced Spektor et al., application utilizes a motor 39-driven eccentric cam 41 which contacts a roller 42 mounted to the bearing block 29.
According to the Spektor, et al., application, the heater is maintained at a selected temperature and is maintained in contact with the dry film 13 for a selected period to achieve film development. A timer (not shown) is actuated by the crescent wheel 43 along with an LED and photodetector mounted within the element 44. In the rest position, the edge 46 of the crescent wheel 43 is on the left side of the LED beam. When the motor is started the beam is broken by the crescent wheel 43 until the edge 47 appears on the right side of the beam, at which time the bearing block is in its uppermost position. The bearing block remains in that position for the required development time and then is driven to its rest position awaiting the next aperture card.
Referring further to FIGS. 3 and 4, a drive mechanism 50 is used to urge the aperture card into the correct position for developing. This mechanism includes two sets of spring-loaded pinch rollers comprising a first and second roller, 51 and 52, respectively, loaded by springs 53. The bottom set of rollers 52 is driven by a shaft 54 which in turn is driven by a pulley 56 via a drive belt (not shown).
While the referenced dry film developer has satisfied its design objectives, as usually occurs, some improvement is desired. In this case, it is desirable to provide even better image control. That is, it would be useful to provide improved image uniformity by eliminating image smearing, which is characterized by horizontal lines 18, FIG. 1, being broadened at their ends.